Commodore 64 Capacitor Replacement Guide

Recapping a Commodore 64 (all board revisions) restores stable power rails, lowers heat-stress on MOS chips and cures many “mystery” crashes, video glitches and SID noise. Because every C64 relies on an external +5 V DC / 9 VAC “brick” the on-board capacitors don’t fail quite as catastrophically as in computers with internal switch-modes, yet forty-year-old aluminium electrolytics are now well past their design life.

Visual Inspection & Failure Signs

• Bulging or leaning cans – especially the tall 4 700 µF reservoir (C88/C89).
• Leakage residue – brown/green crust at base of C90 (colour-RAM decoupler) is common.
• Ripple / hum on audio – audible buzz that follows screen brightness often tracks to dried-out C13 (SID analogue rail) or the RF-modulator’s 100 µF pair.
• Intermittent reset when warm – C15 (10 µF reset RC) high-ESR causes POR threshold to mis-trip.

If one capacitor shows trouble, replace all electrolytics on the board.

Commodore 64 Logic-Board Capacitor Lists

Unlike the VIC-20, the C64 underwent five major PCB generations. Commodore kept reference numbers fairly consistent, but always cross-check your silkscreen.

“Long boards” – Assy 326298 / 250407

Early C64 Electrolytic Capacitors

Board ref	Capacitance	Voltage	Purpose / rail
C88	4 700 µF	16 V	Main +5 V bulk (from external PSU)
C90	1 000 µF	16 V	Secondary 5 V at VIC/SID (reduces raster-noise)
C91	470 µF	25 V	+12 V filter (SID 6581 & VIC 6567/9 analogue)
C13	220 µF	25 V	9 VAC ► +12 V doubler reservoir
C14	100 µF	16 V	9 VAC ► 5 V gate-array supply (PLA decouple)
C15	10 µF	16 V	Power-on reset RC
C38	22 µF	16 V	Audio path (SID DC-blocking)
C70	3.3 µF	50 V	Chroma-coupling into RF modulator
C71,C72	100 µF	16 V	RF modulator 5 V and audio buffer

Very early NTSC boards mark C90 as 2 200 µF – Commodore standardised on 1 000 µF by Rev-B.

Assy 250425 – first “cost-reduced” long board

Same parts list as 250407 except C91 is omitted (12 V rail deleted when 8580 SID not yet adopted but cost saving began). Replace values exactly as found.

Assy 250466 – transitional board (8-chip DRAM → 2-chip DRAM)

250466 Capacitors

Ref	Capacitance	Voltage	Notes
C88	3 300 µF	16 V	Commodore shaved value; 4 700 µF fits & improves ripple
C90	470 µF	16 V	Lower current draw of HMOS chips allowed smaller part
C91	220 µF	25 V	+12 V still present for 6581 SID (last board to use it)
Others	identical	–	Replace like-for-like

“Short boards” – Assy 250469 (A/B/C) & 250469-Aldi

Short-Board Capacitor Set

Ref	Capacitance	Voltage	Rail / circuit
C88	2 200 µF	10 V	Bulk +5 V (HMOS load ≈ 600 mA)
C89	1 000 µF	10 V	Local decouple for VIC-II (8562/8565)
C90	330 µF	10 V	SID 8580 analogue +9 V
C91	*n/a*	–	12 V rail deleted; do not fit tall cans!
C15	10 µF	16 V	Reset timer (value unchanged)
C38	47 µF	16 V	Audio DC-block (lower because 8580 output bias differs)
C70	2.2 µF	50 V	Chroma-coupling (smaller foil can type)
C71,C72	47 µF	16 V	RF modulator local filters

The 250469-Aldi variant adds a linear 7812 + 470 µF 16 V can (C92) to power a 6581 SID on an otherwise 5 V-only board. If present, replace that extra capacitor as well.

Recapping Procedure

1. Disassemble : remove three rear screws, two under the keyboard, pop keyboard hinges.
2. Remove RF shield : desolder the six folded-tabs or snip and replace with screws on re-assembly.
3. Label keyboard & LED leads.
4. Desolder each capacitor with braid + flux. Commodore used thick, high-temperature solder; 375 °C is usually required.
5. Fit new capacitors, matching polarity and lead-spacing (5 mm on small cans, 7.5 mm on main filters). Keep height ≤ 17 mm so the metal shield clears.
6. Clean flux, inspect for bridges.
7. First power-up through a current-limited bench supply or a C64 Saver inline protector in case the original brick is bad.

Post-Recap Voltage / Ripple Checks

Expected Rails – BASIC READY prompt, no cartridge

Test point (scope @20 MHz)	Long board	Short board	Max ripple (p-p)
+5 V (U6 PLA pin 24)	4.95 – 5.10 V	same	< 50 mV
+12 V (SID pin 28)	11.5 – 12.6 V	–	< 120 mV
+9 V (SID pin 28, 8580)	–	8.7 – 9.3 V	< 100 mV
9 VAC (user-port pins 10/11)	8.5 – 10 V rms	same	sine-like

A VIC-II picture that jitters or vertical “rainbow lines” usually means > 150 mV of 5 V ripple.

Recommended Tools & Parts

• 70 W temperature-controlled iron (2 mm chisel tip).
• Solder-wick and spring pump – double-layer ground pads are stubborn.
• Leaded 63/37 or SAC-lead-free solder (avoid cheap flux-core that leaves residue).
• 105 °C, low-ESR radial capacitors (Nichicon PW/PS, Panasonic FR/FC, Rubycon ZLH).
• IPA, nylon brush, Kapton tape to insulate cap cans that sit against the RF shield.

Extra Tips

• Check the brick first ! An over-voltage PSU kills fresh caps (and PLA / RAM) instantly.
• SID heat-pad : early boards rely on C90 as a “heat-sink standoff” – keep replacement can the same diameter so the RF-shield pad still contacts the SID.
• Retain RF modulator? If you have done an S-video or composite-bypass mod, you may delete C70/71/72 and the entire modulator 5 V line.
• Socket inspection : reseat VIC-II, SID, PLA after the recap – temperature swings often unseat them.
• Re-cap the 1541-II brick if bundled; its 4 700 µF can is the same age.

Related Pages

• Commodore 64 Troubleshooting Guide
• Commodore 64C Troubleshooting Guide
• Commodore 64 Power-Supply Protector (C64 Saver)